[C++-sig] errors compiling Boost Python example

[Joel Uckelman]

I'm trying to compile the example from the Boost Python docs without
success.

hello.cpp:

  #include <boost/python.hpp>

  char const * const greet() {
    return "hello, world";
  }

  BOOST_PYTHON_MODULE(hello_ext) {
    using namespace boost::python;
    def("greet", greet);
  }

I have Boost 1.48, Python 2.7, and gcc 4.7.0.

When I do this:

  g++ -fPIC -I/usr/include/python2.7 -c -o hello.o hello.cpp

I get the following errors:

In file included from /usr/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:47:0,
                 from /usr/include/boost/python/detail/invoke.hpp:63,
                 from /usr/include/boost/python/detail/caller.hpp:16,
                 from /usr/include/boost/python/object/function_handle.hpp:8,
                 from /usr/include/boost/python/converter/arg_to_python.hpp:19,
                 from /usr/include/boost/python/call.hpp:15,
                 from /usr/include/boost/python/object_core.hpp:14,
                 from /usr/include/boost/python/args.hpp:25,
                 from /usr/include/boost/python.hpp:11,
                 from hello.cpp:1:
/usr/include/boost/python/detail/invoke.hpp: In instantiation of ‘PyObject* boost::python::detail::invoke(boost::python::detail::invoke_tag_<false, false>, const RC&, F&) [with RC = boost::python::detail::specify_a_return_value_policy_to_wrap_functions_returning<const char* const>; F = const char* const (*)(); PyObject = _object]’:
/usr/include/boost/python/detail/caller.hpp:223:13:   required from ‘PyObject* boost::python::detail::caller_arity<0u>::impl<F, Policies, Sig>::operator()(PyObject*, PyObject*) [with F = const char* const (*)(); Policies = boost::python::default_call_policies; Sig = boost::mpl::vector1<const char* const>; PyObject = _object]’
/usr/include/boost/python/object/py_function.hpp:38:33:   required from ‘PyObject* boost::python::objects::caller_py_function_impl<Caller>::operator()(PyObject*, PyObject*) [with Caller = boost::python::detail::caller<const char* const (*)(), boost::python::default_call_policies, boost::mpl::vector1<const char* const> >; PyObject = _object]’
hello.cpp:10:1:   required from here
/usr/include/boost/python/detail/invoke.hpp:75:19: error: no match for call to ‘(const boost::python::detail::specify_a_return_value_policy_to_wrap_functions_returning<const char* const>) (const char*)’
In file included from /usr/include/boost/python/object/function_handle.hpp:8:0,
                 from /usr/include/boost/python/converter/arg_to_python.hpp:19,
                 from /usr/include/boost/python/call.hpp:15,
                 from /usr/include/boost/python/object_core.hpp:14,
                 from /usr/include/boost/python/args.hpp:25,
                 from /usr/include/boost/python.hpp:11,
                 from hello.cpp:1:
/usr/include/boost/python/detail/caller.hpp: In instantiation of ‘static const PyTypeObject* boost::python::detail::converter_target_type<ResultConverter>::get_pytype() [with ResultConverter = boost::python::detail::specify_a_return_value_policy_to_wrap_functions_returning<const char* const>; PyTypeObject = _typeobject]’:
/usr/include/boost/python/detail/caller.hpp:242:13:   required from ‘static boost::python::detail::py_func_sig_info boost::python::detail::caller_arity<0u>::impl<F, Policies, Sig>::signature() [with F = const char* const (*)(); Policies = boost::python::default_call_policies; Sig = boost::mpl::vector1<const char* const>]’
/usr/include/boost/python/object/py_function.hpp:48:35:   required from ‘boost::python::detail::py_func_sig_info boost::python::objects::caller_py_function_impl<Caller>::signature() const [with Caller = boost::python::detail::caller<const char* const (*)(), boost::python::default_call_policies, boost::mpl::vector1<const char* const> >]’
hello.cpp:10:1:   required from here
/usr/include/boost/python/detail/caller.hpp:102:109: error: ‘struct boost::python::detail::specify_a_return_value_policy_to_wrap_functions_returning<const char* const>’ has no member named ‘get_pytype’
In file included from /usr/include/boost/python/converter/pytype_function.hpp:10:0,
                 from /usr/include/boost/python/to_python_indirect.hpp:16,
                 from /usr/include/boost/python/converter/arg_to_python.hpp:10,
                 from /usr/include/boost/python/call.hpp:15,
                 from /usr/include/boost/python/object_core.hpp:14,
                 from /usr/include/boost/python/args.hpp:25,
                 from /usr/include/boost/python.hpp:11,
                 from hello.cpp:1:
/usr/include/boost/python/detail/unwind_type.hpp: In instantiation of ‘typename Generator::result_type boost::python::detail::unwind_type(boost::type<U>*, Generator*) [with Generator = boost::python::converter::detail::unwind_type_id_helper; U = const char* const; typename Generator::result_type = boost::python::type_info]’:
/usr/include/boost/python/converter/pytype_function.hpp:45:74:   required from ‘boost::python::type_info boost::python::converter::detail::unwind_type_id_(boost::type<T>*, mpl_::false_*) [with T = const char* const; mpl_::false_ = mpl_::bool_<false>]’
/usr/include/boost/python/converter/pytype_function.hpp:68:13:   required from ‘static const PyTypeObject* boost::python::converter::expected_pytype_for_arg<T>::get_pytype() [with T = const char* const; PyTypeObject = _typeobject]’
/usr/include/boost/python/detail/signature.hpp:98:13:   required from ‘static const boost::python::detail::signature_element* boost::python::detail::signature_arity<0u>::impl<Sig>::elements() [with Sig = boost::mpl::vector1<const char* const>]’
/usr/include/boost/python/detail/caller.hpp:232:78:   required from ‘static boost::python::detail::py_func_sig_info boost::python::detail::caller_arity<0u>::impl<F, Policies, Sig>::signature() [with F = const char* const (*)(); Policies = boost::python::default_call_policies; Sig = boost::mpl::vector1<const char* const>]’
/usr/include/boost/python/object/py_function.hpp:48:35:   required from ‘boost::python::detail::py_func_sig_info boost::python::objects::caller_py_function_impl<Caller>::signature() const [with Caller = boost::python::detail::caller<const char* const (*)(), boost::python::default_call_policies, boost::mpl::vector1<const char* const> >]’
hello.cpp:10:1:   required from here
/usr/include/boost/python/detail/unwind_type.hpp:165:72: error: no matching function for call to ‘boost::python::detail::unwind_helper2<1>::execute(const char* const (*)(), boost::python::converter::detail::unwind_type_id_helper*)’
/usr/include/boost/python/detail/unwind_type.hpp:165:72: note: candidate is:
In file included from /usr/include/boost/python/converter/pytype_function.hpp:10:0,
                 from /usr/include/boost/python/to_python_indirect.hpp:16,
                 from /usr/include/boost/python/converter/arg_to_python.hpp:10,
                 from /usr/include/boost/python/call.hpp:15,
                 from /usr/include/boost/python/object_core.hpp:14,
                 from /usr/include/boost/python/args.hpp:25,
                 from /usr/include/boost/python.hpp:11,
                 from hello.cpp:1:
/usr/include/boost/python/detail/unwind_type.hpp:114:5: note: template<class Generator, class U> static typename Generator::result_type boost::python::detail::unwind_helper2<1>::execute(U* (*)(), Generator*)
/usr/include/boost/python/detail/unwind_type.hpp:114:5: note:   template argument deduction/substitution failed:
In file included from /usr/include/boost/python/converter/pytype_function.hpp:10:0,
                 from /usr/include/boost/python/to_python_indirect.hpp:16,
                 from /usr/include/boost/python/converter/arg_to_python.hpp:10,
                 from /usr/include/boost/python/call.hpp:15,
                 from /usr/include/boost/python/object_core.hpp:14,
                 from /usr/include/boost/python/args.hpp:25,
                 from /usr/include/boost/python.hpp:11,
                 from hello.cpp:1:
/usr/include/boost/python/detail/unwind_type.hpp:165:72: note:   types ‘U*’ and ‘const char* const’ have incompatible cv-qualifiers



It looks like the salient error is this one:

/usr/include/boost/python/detail/invoke.hpp:75:19: error: no match for call to ‘(const boost::python::detail::specify_a_return_value_policy_to_wrap_functions_returning<const char* const>) (const char*)’

but the Boost Python tutorial didn't mention the need to specify a
return value policy for the "hello world" example.

So, I suppose this is either 

a) a bug in Boost Python,
b) a bug in the Boost Python tutorial I copied from, or
c) a mistake I'm making

Does anyone see which?

-- 
J.